The present invention relates to an optical image stabilizer provided in optical apparatuses including an image-pickup apparatus such as a video camera, a digital still camera and a film camera, and observation apparatuses such as a binocular, a telescope, and a fieldscope.
Optical apparatuses of the abovementioned type are often equipped with an optical image stabilizer for reducing image shake due to hand jiggling. The optical image stabilizer detects movements of the optical apparatus with a vibration sensor such as an acceleration sensor and an angular velocity sensor and moves a correction lens in a plane orthogonal to an optical axis based on the detection result, thereby reducing displacements of an image on an image plane. The correction lens is generally driven by using an electromagnetic actuator formed of a magnet and a coil.
In the optical image stabilizer, it is necessary that the correction lens should be held to be freely moved in parallel with the plane orthogonal to the optical axis and should be prevented from rotating about the optical axis in order to accurately perform driving and position control with the actuator.
An optical image stabilizer disclosed in Japanese Patent Laid-Open No. 11(1999)-258651 includes a guide mechanism for preventing the rotation of the correction lens about the optical axis. In addition, any backlash of the guide mechanism is reduced through biasing by a spring to minimize vibrations in image-shake correction operation and reduce noise in driving.
Japanese Patent Laid-Open No. 10(1998)-197911 has disclosed an optical image stabilizer that prevents the rotation of the correction lens about the optical axis by using an L-shaped guide shaft. The guide shaft guides the correction lens in a direction at an angle of 45 degrees with respect to the direction of driving by the actuator.
In each of the optical image stabilizers disclosed in Japanese Patent Laid-Open No. 11(1999)-258651 and No. 10(1998)-197911, the guide mechanism for preventing the rotation of the correction lens about the optical axis causes the correction lens to move in parallel through sliding. This presents a problem in which sliding friction produced in the guide mechanism reduces driving responsivity especially when the correction lens is driven slightly.
To address this, Japanese Patent Laid-Open No. 2004-101721 has disclosed an optical image stabilizer that prevents the rotation of the correction lens about the optical axis by using a ball that can be rolled. The stabilizer includes a guide member that has V-shaped groove portions formed in both surfaces thereof and extending in directions orthogonal to each other. The stabilizer also has a ball (steel ball) placed in the V-shaped groove portion in one of the surfaces of the guide member and sandwiched between the groove portion and a base member of the stabilizer and a ball placed in the V-shaped groove portion in the other of the surfaces and sandwiched between the groove portion and a lens-holding member for holding the correction lens.
In the optical image stabilizer disclosed in Japanese Patent Laid-Open No. 2004-101721, the surfaces of the guide member have the V-shaped groove portions formed therein, while the surfaces of the base member and the lens-holding member in contact with the balls are formed as flat surfaces. Since rolling friction of the balls is smaller than sliding friction, the balls are rolled without sliding on the flat surfaces in contact therewith when small shakes or low-frequency shakes are applied to the stabilizer. This can favorably prevent the rotation of the correction lens about the optical axis and reduction in driving responsivity due to the sliding friction.
However, when large-amplitude shakes or high-frequency shakes are applied or a large external force (torque) in the rotation direction is applied to the stabilizer, the balls are slid on the surfaces in contact therewith, and rotation of the correction lens about the optical axis is not prevented.